The present invention relates to a disk apparatus which can increase a memory capacity and can realize a small and thin shape and, more particularly, to a small disk apparatus using a disk medium of 2.5 inches.
The invention relates to a disk apparatus of a sector servo system for positioning a head on the basis of servo information recorded on a data surface and, more particularly, relates to a disk apparatus which accurately detects a sector mark and a gray code indicative of a cylinder address which have been recorded in a servo frame at the head of a sector together with servo information.
Further, the invention relates to a data processing apparatus including a disk apparatus which is controlled by a microprocessor and also relates to a power saving method of such an apparatus. More particularly, the invention relates to a data processing apparatus in which a program memory is constructed by a ROM and a RAM of different electric power consumptions and also relates to a power saving method of such an apparatus.
In recent years, a small hard disk has been installed as an external memory apparatus of a notebook type computer or a portable communication terminal. As such a small hard disk, for example, a hard disk having therein two or three small disk media of 2.5 inches is used. In such a small disk apparatus, in addition to an enlargement of a memory capacity, a miniaturization, a light weight, and a thin shape of the apparatus are further requested. The miniaturization, light weight, and thin shape of the disk apparatus reduce an installation space when the apparatus is installed in a notebook type computer or the like. The whole computer including a magnetic disk apparatus is miniaturized and can be easily carried. Further, drive loads of a spindle motor and a voice coil motor are reduced, so that the electric power consumption can be saved. The notebook type computer or portable communication terminal can operate by a battery power source. The performance is, therefore, decided by a period of time during which the computer or terminal can be used without charging the battery. Thus, when the electric power consumption of the disk apparatus decreases, the battery's usable time increases by a time corresponding to such a decreased power consumption and the performance is improved. In order to further accomplish a small size, light weight, and thin shape of the disk apparatus, however, there are the following various problems.
In an actuator of the in-line type for positioning a head, an arm portion for supporting the head is provided at one end of a rotary shaft and a movable coil of a voice coil motor is provided at the other end of the rotary shaft. The actuator must accomplish both the light weight and a balance between the head side and the coil side. Particularly, in recent years, the actuator has an asymmetrical arm shape in which the front edge of the arm is bent to the disk center side in a manner such that even if the rotational position of the actuator changes, the head direction does not largely deviate from the track tangent line. Thus, in addition to a balance adjustment in the front/rear direction, a balance in the right/left direction in association with the asymmetrical arm shape has to be obtained. Hitherto, such a balance adjustment is performed by a weight adjustment such as to change the thicknesses of the right and left portions of the movable coil on the installation side, or the like. However, designing works to simultaneously adjust both the balance in the front/rear direction and the balance in the right/left direction of the actuator by adjusting the thicknesses is complicated. There is a problem such that even if the weight balance is obtained, the shape balance is largely lost, or the like.
In the voice coil motor for driving the actuator of the head, a yoke having a permanent magnet is fixed and arranged to a casing base for the movable coil on the actuator side. Hitherto, the yoke side having the permanent magnet is assembled and fixed by screws, an adhesive agent, caulking, or the like. Therefore, the number of parts and the number of assembling steps increase and the assembling works are complicated.
In the conventional voice coil motor, the magnet on the yoke side is set to the same size as that of each of the coil portions on the right and left sides of the rectangular movable coil on the actuator side, thereby allowing a magnetic flux to pass through the coil effective portion to generate a rotational torque. A magnetic flux density of the coil at the edge portion of the magnet decreases, however, due to a leakage magnetic flux and the coil effective length is not fully used.
In the disk apparatus, generally, the actuator on the movable side and the circuit board on the fixed side are coupled by a connecting band of a flexible printed circuit (hereinlater, referred to as `FPC`). In this case, the assembling work to position and fix the FPC connecting band to the fixed side is important. When there is a small mistake in the assembling work, a variation easily occurs in the bending state of the FPC connecting band by the driving of the actuator, so that there are problems such that a force that is applied to the actuator abnormally changes, the FPC connecting band shakes and may come into contact with the parts such as IC, resister, and the like during the driving.
An MR head using a magnetoresistive device is used as a read head in order to improve a recording density by reducing a track pitch of the disk medium. In the reading operation of the MR head, in order to assure a high S/N ratio of an ultra weak read signal, a specified DC bias current is supplied to the MR head. When the bias current flows in the MR head, a head core has a potential. In the case where the head core comes into contact with the disk medium, there is a danger such that the current flows between the core and the disk medium and the head core are destructed. To avoid such a situation, it is necessary for the disk medium to have the same potential as that of the head core. Hitherto, the signal line is independently arranged from a circuit portion which is fixedly installed to the actuator side and the bias voltage is also supplied to the disk medium. Therefore, there are problems such that the parts arrangement is complicated and the number of working steps also increases by an amount corresponding to that an exclusive-use bias supply line is provided and further, an external force due to the exclusive-use bias line is applied to the actuator.
Further, in case of using the MR head as a read head, there is a problem such that when the read signal passes in the circuit pattern formed on the FPC connecting band, external noises are superimposed on the circuit pattern as induction noises, so that the S/N ratio deteriorates.
Further, in association with the supply of the bias to the MR head in the reading operation, a disk enclosure itself having the disk mechanism therein has a certain potential. For instance, when the disk apparatus is assembled as an external memory apparatus into the notebook type computer, a problem such that the apparatus has to be insulated from the assembled apparatus newly occurs.
In the small hard disk, an exclusive-use servo surface on which the servo information for positioning the head has been recorded as in the conventional large disk apparatus cannot be provided. A sector servo system in which the servo information has been recorded on the data surface is used. For example, one cylinder is divided into 60 sectors and a servo frame is recorded to the head of each sector. A sector mark indicative of the servo frame, a gray code to detect a cylinder address, an index pattern (only for the head sector), an AGC pattern to set an AGC level of a reading amplifier, and a servo pattern to detect the head position are magnetically recorded in the servo frame.
In the disk apparatus using the sector servo system, since a data area in the sector can be enlarged as the servo frame is short, it is desired to minimize each pattern which is recorded in the servo frame in order to increase the memory capacity.
On the contrary, in order to raise a precision of the pattern detection of the sector mark, gray code, or the like recorded in the servo frame, a recording pitch in the cylinder direction per pattern is enlarged. For example, the sector mark has a recording pattern of "N.quadrature.S.quadrature.NS". When a recording period that is decided by a reference clock assumes (T), it is recorded as "16T, 16T, 10T, 10T" and an interval of total 52T is needed.
For example, when one bit width is equal to 6T, in the gray code that is recorded subsequent to the sector mark, 14 bits of "G12, G11, . . . , G0, GH" are recorded by the gray code "X000X000". The gray code has a length of 84T. Further, an interval of about 160T is necessary as a position area. Thus, an interval of 196T is needed as a whole servo frame.
Now, assuming that an interval between one servo frame and the next servo frame is equal to 3600T, the servo area occupies 5.4% of one track. By shortening the sector mark and gray code, the memory capacity can be increased. However, when the sector mark and gray code are shortened, the pattern detecting precision deteriorates. Therefore, there is a limitation in length of each of the sector mark and gray code.
On the other hand, in the conventional disk apparatus using the sector servo system, a deviation value due to an eccentricity of the disk medium is measured and the eccentricity is corrected at the time of an on-track control. In the measurement of the eccentricity correction value for this purpose, a command for the eccentricity correction is generated every predetermined time and a deviation amount from the track center is stored into an RAM or the like. In an ordinary on-track control, the deviation amount which has already been measured is subtracted from the target position and the on-track control is performed, thereby enabling the head to be always positioned to the track center.
Since the eccentricity correction value, however, is measured every predetermined time, the correction is performed with the previous measurement value for a period of time between the measurement and the subsequent measurement, so that the invention cannot cope with the eccentricity due to a temperature change or the like.
Further, in the disk apparatus using the sector servo system, since servo frames have fixedly been recorded on the cylinder, the sector size is basically fixed. However, in order to enable a data block exceeding a fixed sector length or a plurality of the data blocks which can be put into the fixed sector length to be handled, it is actually necessary to use a variable sector size which can vary the generating position of the sector pulse.
In addition to the data block size, the process for making the sector size variable ignores a defective sector and makes an exchanging process unnecessary so that the apparatus has to cope with various requests such as slipping process for inhibiting the generation of the sector pulse and, further, a generation of the sector pulse which is completely synchronized with the servo frame at the time of a digital error test, and the like.
In the hard disk which is installed in a notebook type computer or the like, a minimum program necessary to make the system operative is generally stored in an ROM (read only memory). A dynamic RAM (hereinlater, referred to as "DRAM") which is cheap in costs is used to store control programs which are used for a seeking process and reading and writing processes. The control program is downloaded from the disk medium to the DRAM when the system is made operative.
As one of the performances of a portable apparatus such as a notebook type computer, there is an operable time by a battery power supply. It is desired to extend the operable time by the battery power supply as much as possible. Consequently, with respect to an external memory apparatus such as a hard disk or the like which is installed in the notebook type computer, the apparatus of a small electric power consumption is desired.
When a microprocessor uses a DRAM and operates in a hard disk, a refreshing operation for rewriting data which was written or read to/from the DRAM is needed interlockingly with the reading or writing operation. Therefore, a current consumption of the DRAM increases to, for example, 150 mA at the time of the reading and writing operations and the refreshing operation. The current consumption of the DRAM is equal to about 1 mA when there is no access and the electric power consumption increases when the number of accesses increases.
Therefore, the electric power which is consumed when using the program on the memory constructed by the ROM is smaller than when using the program on the memory constructed by the DRAM. Therefore, it is considered that all of program memories are constructed by the ROMs in order to reduce the power consumption.
In case of constructing all of the program memories by only ROMs, however, there is a problem such that the apparatus cannot correspond to a program change such as a version-up or the like. Since the ROM cannot correspond to a revised version (program change), the apparatus has been programmed so as to access to the DRAM except in the modes other than the initial loading.
Although it is also considered to use a rewritable non-volatile EEPROM, since the costs rise, it is difficult to realize such an apparatus.